The present invention relates to semiconductor light emitting devices and processes for producing same. More particularly, the present invention relates to a semiconductor light emitting device, a display unit, a method of fabricating a semiconductor light emitting device, and a method of fabricating a semiconductor laser having wurtzite type compound semiconductor layers such as GaN based semiconductor layers that are formed by selective growth.
Conventionally, when manufacturing a semiconductor light emitting device, a semiconductor laser device or a light emitting diode is fabricated by forming a selection mask on a sapphire substrate and selectively growing a semiconductor layer made from a nitride such as gallium nitride through an opening in the selection mask. Sapphire is often used as a substrate for growing gallium nitride. However, dislocations often occur in the crystals, at a high density, due to mismatches between the crystal lattices of the sapphire substrate and gallium nitride. The following methods are known to reduce crystal defects: a method of forming a low temperature buffer layer on a substrate; a method of combining usual crystal growth with selective crystal growth in the lateral direction (ELO: Epitaxial Lateral Overgrowth as described in Japanese Patent Laid-open No. Hei 10-312971); and a method of forming a gallium nitride based semiconductor laser, in which stacked layers having tilt planes are formed by selective growth (see Japanese Patent Laid-open No. Hei 11-312840).
Conventionally, an image display unit is configured by arranging pixels in a matrix. Each pixel is composed of a combination of light emitting diodes or semiconductor lasers of blue, green and red. An image is displayed by independently driving the respective pixels. The image display unit can be also used as a white light emitting unit or an illumination unit by allowing the light emitting devices of blue, green, and red to simultaneously emit light of blue, green, and red. In particular, since a light emitting device using a nitride based semiconductor has a band gap energy ranging from about 1.9 eV to about 6.2 eV, a number of light emitting devices capable of emitting light of many colors can be fabricated using only semiconductor layers made from one kind of material (i.e., the nitride based semiconductor), thereby easily realizing a full-color display. Multi-color light emitting devices using nitride based semiconductors have been studied extensively. It is to be noted that the term “nitride” used herein describes a compound which contains one or more of B, Al, Ga, In, and Ta as group III elements and N as a group V element, and which may contain impurities in an amount of about 1% or less of the total amount or about 1×1020 cm3 or less.
In the above-described method, which makes use of selective crystal growth in the lateral direction for reducing through-dislocations from a substrate, and in the crystal growth method, in which a facet structure is formed in a growth region for reducing through-dislocations from a substrate, it is possible to bend through-dislocations from a substrate in the lateral direction by the facet structure portion or the like, and hence to significantly reduce crystal defects. However, to form a light emission region including an active layer after selective crystal growth in the lateral direction or formation of the facet structure, the selective crystal growth in the lateral direction must be further continued or the facet structure is buried in order to obtain a flat plane on which the light emission region is to be formed. As a result, the number of processing steps is increased and the time required for fabricating the device is prolonged.
The above-described gallium nitride based semiconductor laser and its fabrication method are disclosed in Japanese Patent Laid-open No. Hei 11-312840. When manufacturing a device according to this method, a conductive selection mask is formed in an approximately center portion of an opening portion of an insulating selection mask, to obtain a stacked structure having a triangular shape in cross-section formed by selective growth. In such a semiconductor laser, however, the stacked structure having the triangular shape in cross-section is only used as a high resistance region for concentrating a current at an active layer located at the center portion. Therefore, even though a (1-101) plane (which is called an S-plane) appearing on a tilt or a slant plane is excellent for repeatability of fabrication, a region as the active layer is limited to the vicinity of the conductive selection mask at the central portion held by the stacked structure having the triangular shape in cross-section. Accordingly, it is difficult to control a film quality of the active layer. As a result, the repeatability of the fabrication of the whole device is degraded.